Device for Hardening a Mechanical Propulsion System Connection for a Mortar Round and Round Comprising Such a Connection

ABSTRACT

A self-propelled munition having a munition rear body of circular cylindrical shape of diameter D 1 , along axis ZZ′. A propulsion system of the munition has a tubular casing of circular cross section, has an axis of revolution coincident with axis ZZ′, has an internal surface of diameter D 1  able to slide over said munition rear body, and contains a pyrotechnic propulsion chamber. The munition includes a mechanical connection between the propulsion system and the munition using shear pins evenly distributed about axis ZZ′, a hardened mechanical connection having a ring groove around the munition rear body in a plane perpendicular to axis ZZ′, another ring groove on the internal surface of the propulsion system casing, a retaining ring inserted in the ring groove configured to expand into the other ring groove from diameter D 1  to a diameter greater than diameter D 1  to secure the propulsion system to the munition.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to foreign French patent application No. FR 1004718, filed on Dec. 3, 2010, the disclosure of which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to munitions of the self-propelled type and notably to a device for automatically hardening a mechanical connection between the munition and its propulsion system.

BACKGROUND

Self-propelled artillery rounds are, for example, missiles, rockets or guided and/or long range self-propelled weapons. The munition propulsion system comprises a propellant pyrotechnic charge which will be active when the munition is in use.

These types of self-propelled munitions need to meet low-vulnerability requirements. To this end, they need to be designed and produced so as to resist, or at least minimize, pyrotechnic reactions caused by influences external to the munition and to the propulsion system such as the heat caused by a fire, a fuel fire, slow heating by external or climatic causes, bullet impact, impacts of light or heavy fragments of other munitions, the effect of a hollow charge, of the munition being dropped from a height of 12 meters and need to be able to resist other influences or effects that could activate the pyrotechnic charge in the propulsion system and to assure against sympathetic detonation. The low vulnerability status of the munition has furthermore to be sustained throughout the life of the munition, namely from storage until such time as the munition is fired.

The choice of compositions used in the pyrotechnic charge of the propulsion system, notably in terms of sensitivity to initiation, the choice of materials, mechanical properties and geometry such as the thickness of the propulsion system casing containing the propellant charge plays a large part in achieving the low-vulnerability requirements.

In self-propelled munitions of the prior art, the munition is firmly attached to the propulsion system by rigid connections so as to ensure that the munition will operate normally when fired. The propulsion systems in these types of munition of the prior art comprise deconfinement safety features, for example thinning of material in certain regions of the wall of the propulsion system in order to release the gases of accidental combustion of the pyrotechnic charge. The pressure needed to rupture the wall of the propulsion system for the purposes of deconfinement needs to be very high indeed in order not to impair its propulsion capability in normal operation, and this represents a danger to the personnel when handling or storing the self-propelled munition. Further, the low vulnerability status of this type of munition of the prior art is not always assured over the longer term.

SUMMARY OF THE INVENTION

In order to alleviate the disadvantages of the munitions of the prior art, the invention proposes a self-propelled munition intended to be fired against a target, comprising, a munition having a munition body extended by a munition rear body of circular cylindrical shape of diameter D1, along a longitudinal axis ZZ′, a propulsion system of the munition having a casing in the form of a tube of circular cross section of diameter D2, of axis of revolution coincident with the longitudinal axis ZZ′, the casing, having an internal surface of the same diameter D1 as the munition rear body, being able to slide over said munition rear body along said longitudinal axis ZZ′, the casing containing a pyrotechnic propulsion chamber intended to be activated upon firing, characterized in that it comprises at least two mechanical connections each able to adopt an activated state that secures the propulsion system to the munition or a deactivated state that releases the propulsion system from the munition,

the first mechanical connection comprising several shear pins, evenly distributed about the longitudinal axis ZZ′, inserted into the casing of the propulsion system and into the munition rear body, said first mechanical connection moving from an activated state to a deactivated state through the breakage of the shear pins,

the second mechanical connection having a ring groove around the munition rear body in a plane perpendicular to the longitudinal axis ZZ′, another ring groove on the internal surface of the propulsion system casing, a retaining ring inserted in the ring groove, the retaining ring being configured to expand into the other ring groove from the diameter D1 to a diameter D4 that is greater than the diameter D1, and place said second mechanical connection in the activated state.

In one configuration of the self-propelled munition, in a storage phase, the first mechanical connection is in the activated state, the intact pins securing the propulsion system to the munition in terms of rotational and translational movement.

In another configuration, in a munition firing phase, a sliding of the casing over the munition rear body toward said munition body places the first mechanical connection in the deactivated state by the breakage of the shear pins, the second mechanical connection in the activated state through the expanding of the retaining ring into the other ring groove which comes to face the ring groove during said sliding of the casing over the munition rear body.

In another configuration, during a propulsion system deconfinement phase, a sliding of the casing over the munition rear body away from the munition body through an increase in pressure caused by the gases of combustion in the pyrotechnic chamber, places the first mechanical connection in the deactivated state by the breaking of the shear pins and the pyrotechnic chamber in contact with the external surroundings in order to release the combustion gases.

In one embodiment, the munition rear body comprises, on each side of the longitudinal axis ZZ′, two notches and the propulsion system casing comprises two pegs, one peg being inserted into one respective notch on each side of said longitudinal axis ZZ′ to secure the munition and the propulsion system in terms of rotation about the axis ZZ′.

In one embodiment of the self-propelled munition, the casing is delimited, on the munition side, by a casing edge in a plane perpendicular to the longitudinal axis ZZ′.

In another embodiment, the munition body, of circular cylindrical shape having the same outside diameter D2 as the casing of the propulsion system, is extended inside said casing by the munition rear body in the form of a cylinder of circular cross section of diameter D1 forming an annular shoulder in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body ending in the casing in the form of an end surface in another plane perpendicular to the longitudinal axis ZZ′.

In another embodiment, the casing contains a pyrotechnic chamber containing a propellant pyrotechnic charge, the pyrotechnic chamber comprising walls affording thermal protection to the pyrotechnic charge, one thermal protection wall in the form of a tube, in contact with the internal surface of the casing and closed, on the munition side, by another thermal protection wall perpendicular to the longitudinal axis ZZ′.

In another embodiment, the casing of the propulsion system comprises, at the same end as the other thermal protection wall of the pyrotechnic chamber, a circular cylindrical moving end wall of the same diameter D1 as the internal surface of the casing, of axis of revolution coincident with the longitudinal axis ZZ′, having two faces in planes perpendicular to the axis ZZ′, one face in contact with the thermal protection wall and another face on the munition rear body side having a circular recess for keeping a coil spring along the longitudinal axis ZZ′, the spring being inserted between said moving end wall and the end surface of the munition rear body in order to ensure a distance L1 forming a clearance J1 between the other face of the moving end wall and the munition rear body.

In another embodiment, the casing of the propulsion system comprises holes near the casing edge in a plane perpendicular to the axis ZZ′, the munition rear body having other respective holes in the same plane perpendicular to the axis ZZ′ facing the holes in the casing of the propulsion system for the forcible insertion of the pins, the positions of the holes near the casing edge and those of the other holes in the munition rear body being such that when the pins are inserted into the respective holes in the casing and the munition rear body, the shoulder of the munition body and the casing edge are separated by a distance L2 to form a clearance J2.

In another embodiment, the clearance J2 is smaller than the clearance J1 so that when the pins have sheared upon firing, the casing edge and the shoulder coming into contact, there is still a space between the munition rear body end surface and the other face of the moving end wall.

In another embodiment, the shear strength of the second mechanical connection is greater than the shear strength of the first mechanical connection.

In another embodiment, the shear pins and the retaining ring are secured to the munition by a propulsion system end wall which is itself secured to the propulsion system.

In another embodiment, the propulsion system end wall is in the form of a collar closed by an end wall in a plane perpendicular to the longitudinal axis ZZ′, the circular cylindrical exterior surface of the end wall comprises the shoulder, the holes for the pins, the groove containing the retaining ring and the groove containing the body sealing gasket, the face of the end wall on the propulsion system side having the same role as the end surface.

In another embodiment, a circular cylindrical internal part of the propulsion system end wall has a screw thread for the screw-fastening of the munition rear body which likewise has a screw thread that can be screwed onto the screw thread of the propulsion system end wall.

In another embodiment, the self-propelled munition during its storage, transport and maintenance phase, is fitted with a belt that locks the first mechanical connection in the activated state.

In another embodiment, the locking belt, in the form of a tube with an outside diameter D5 greater than the diameter D2 of the external surface of the propulsion system, partially surrounding the munition body and the casing, comprises an interior part in the form of a collar inserted between the casing and the munition body to prevent them from moving closer to one another.

It is a main objective of the self-propelled munition according to the invention to obtain deconfinement of the propulsion system of the munition with a low pressure of the gases caused by accidental combustion of the pyrotechnic charge of the propulsion system.

It is another objective of the invention to obtain deconfinement of a munition propulsion system that is reliable over the longer term.

It is another objective of the invention to create a mechanical connection between the propulsion system and the munition that can be hardened, automatically, by the thrust generated on the munition upon firing.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood with the aid of some embodiments of munitions of the self-propelled type according to the invention, with reference to the indexed drawings in which:

FIG. 1 a is a partial view in axial section of a mortar round according to the invention comprising a self-hardening mechanical connection;

FIG. 1 b is a view of a detail of FIG. 1 a;

FIG. 1 c is a view of a detail of a variant embodiment of the mortar round according to the invention;

FIG. 2 a is an external view of the region of connection between the munition and the propulsion system of the mortar round of FIG. 1 a;

FIG. 2 b is a perspective view of the region of connection of FIG. 2 a;

FIGS. 3 a and 3 b show two respective steps in the operation of the mortar round of FIG. 1 a as pressure increases in the propulsion system prior to firing;

FIG. 4 a depicts the mortar round of FIG. 1 a in a firing phase;

FIG. 4 b shows an external view of the region of connection between the munition and the propulsion system of the mortar round of FIG. 4 a;

FIG. 5 a depicts the mortar round of FIG. 1 a in a phase of the initiation of its propulsion system;

FIG. 5 b is a view of a detail of FIG. 5 a;

FIG. 6 is a variant embodiment of the hardenable mechanical connection according to the invention for the mortar round of FIG. 1 a; and

FIG. 7 is a partial view in axial section through the mortar round of FIG. 1 a comprising a belt that locks against breakage of the mechanical connection.

DETAILED DESCRIPTION

FIG. 1 a is a partial view in axial section of a mortar round according to the invention, comprising a self-hardening mechanical connection.

FIG. 1 b is a view of a detail of FIG. 1 a.

The mortar round comprises, along a longitudinal axis ZZ′, a munition 10 having a munition body 12, a propulsion system 20 for said munition 10, a first and a second mechanical connection 24 between the munition and the propulsion system. Each of the connections can adopt an activated state that secures the propulsion system 20 to the munition 10 or a deactivated state that releases the propulsion system 20 from the munition 10.

FIG. 1 b shows the region of the mortar round that comprises the mechanical connections, the first mechanical connection essentially comprises shear pins. The second mechanical connection, according to a key principle of the invention, is a self-hardening device, described later on, providing mechanical connection between the munition 10 and the propulsion system 20.

The propulsion system comprises a casing 30 in the form of a tube of circular cross section having an internal surface 31 of inside diameter D1 and an external surface of outside diameter D2. The casing 30 is delimited, on the munition side, by a casing edge 32 in a plane perpendicular to the longitudinal axis ZZ′.

The casing 30 contains a pyrotechnic chamber 33 containing a propellant pyrotechnic charge 34. The pyrotechnic chamber 33 has walls affording thermal protection to the pyrotechnic charge, one thermal protection wall 40 in the form of a tube, in contact with the internal surface 31 of the casing 30 and closed, on the munition side, by another thermal protection wall 44 perpendicular to the longitudinal axis ZZ′.

The munition body 12, of circular cylindrical shape having the same outside diameter D2 of the casing 30 of the propulsion system, is extended inside said casing 30 by a munition rear body 50 in the form of a cylinder of circular cross section of the same diameter D1 as the internal surface of the casing 30 forming an annular shoulder 51 in a plane perpendicular to the longitudinal axis ZZ′. The munition rear body 50 ends inside the casing 30 in the form of an end surface 54 in another plane perpendicular to the longitudinal axis ZZ′. The munition rear body 50 can slide inside the casing 30 along the longitudinal axis ZZ′ and on its surface has a ring groove 56 for the insertion of a retaining ring 58.

The pyrotechnic chamber 33 comprises, at the same end as the other thermal protection wall 44, a circular cylindrical moving end wall 60 of the same diameter D1 as the internal surface of the casing, of axis of revolution coincident with the longitudinal axis ZZ′, having two faces in planes perpendicular to the axis ZZ, one face 61 in contact with the thermal protection wall 44 and another face 62 on the munition body side having a circular recess 63 for keeping a coil spring 64 along the longitudinal axis ZZ′. The spring 64 is inserted between said moving end wall 60 and the end surface 54 of the munition rear body 50 in order to ensure a distance L1 forming a clearance J1 between the other face 62 of the moving end wall 60 and the munition rear body 50.

The mortar round further comprises the first mechanical connection having a series of shear pins 70 inserted into the casing and into the munition body and evenly distributed about the longitudinal axis ZZ′ in a plane Pg perpendicular to the longitudinal axis ZZ′ securing the munition and the propulsion system to one another during a storage or handling phase prior to firing. The activated state of this first mechanical connection corresponds to pins 70 that are intact and not cut through by shear forces, the deactivated state corresponding to the shearing of the pins.

FIG. 2 a shows an external view of the region of connection between the munition and the propulsion system of the mortar round of FIG. 1 a. FIG. 2 b is a perspective view of the region of connection of FIG. 2 a.

If a rifled mortar tube is used, the round is caused to spin as it is ejected from the tube and in such cases, the munition 10 and the propulsion system 20 must remain secured to one another in terms of rotation about the longitudinal axis ZZ′ when the shear pins are cut through, or in the deactivated state, upon firing. For this purpose, the munition rear body 50 comprises, on each side of the longitudinal axis ZZ′, two notches 72, 74 and the casing 30 of the propulsion system comprises two pegs 76, 78, one peg being inserted into one respective notch on each side of the longitudinal axis ZZ′.

The casing 30 of the propulsion system comprises holes 80 near its edge 32 in a plane perpendicular to the axis ZZ′. The munition rear body 50 has other respective holes 82 in one same plane Pg perpendicular to the axis ZZ′, facing the holes 80 in the casing 30 of the propulsion system for the forcible insertion of the pins 70 into the casing 30 and into the munition rear body 50.

The position, along the longitudinal axis ZZ′, of the holes 80 near the edge 32 of the casing 30 and the position of the other holes 82 in the munition rear body 50 are such that when the pins 70 are inserted into the holes 80 in the casing 30 and into the holes 82 in the munition rear body 50, the shoulder 51 of the munition body and the casing edge 32 are separated by a distance L2 to form a clearance J2 (see FIG. 1 b) the function of which is explained later on.

By construction, the clearance J2 has to be smaller than the clearance J1 so that when the pins 70 have sheared during the firing phase, the casing edge 32 and the shoulder 51 coming into contact, there is still a space (or clearance) between the munition rear body 50 end surface 54 and the other face 62 of the moving end wall.

During the munition storage phase, the retaining ring 58, which is in the form of a split ring, of axis of revolution coincident with the longitudinal axis ZZ′, of width E, inserted in the ring groove 56 of the surface of the munition rear body 50, is forcibly kept at the diameter D1 of the casing by said casing 30 covering it. The uncompressed retaining ring 58 before it is fitted between the casing 30 and the munition rear body 50 has a diameter D3 that is greater than the inside diameter D1 of the casing 30, or even greater than the diameter D4.

The retaining ring 58 is, for example, produced in the form of an elastic ring of diameter D3 having edges separated by a distance sufficient that, when the retaining ring is radially compressed, it can adopt the diameter D1 of the internal surface 31 of the casing 30 of the propulsion system.

In order to make the hardened connection between the propulsion system and the munition during the firing phase, the casing 30 on its internal surface 31 has a ring groove 90 of diameter D4 greater than the diameter D1 of the internal surface 31 of the casing 30, of width equal to the width E of the retaining ring 58 so as at least partially to contain the retaining ring 58 as it expands on account of its elasticity to the diameter D4 as the retaining ring 58 is released into said other retaining ring groove 90.

The ring groove 56, the retaining ring 58 and the other ring groove 90 produce the second mechanical connection that forms the self-hardening device for the mechanical connection between the munition and the propulsion system.

This second mechanical connection is in the deactivated state when the retaining ring, during the munition storage phase, is compressed to the diameter D1 between the internal surface of the casing and the munition rear body and is in the activated state as the retaining ring (58) expands into the other ring groove (90) that comes to face the ring groove (56) as the casing (30) slides over the munition rear body (50). This second mechanical connection will not be activated until the munition is being fired.

The distance between the edges of one same side of the one retaining ring groove 56 and the other retaining ring groove 90 is equal to the clearance J2 between the casing edge 32 and the shoulder 51 of the munition body 12 so that during hardening of the propulsion system/munition mechanical connection, the retaining ring 58 comes opposite the other ring groove 90 and expands into this other ring groove 90.

The rear body 50 comprises a body groove 94 containing a body sealing gasket 96 to provide sealing between the munition rear body 50 and the external surroundings.

The moving end wall 60 comprises an end wall groove 98 containing an end wall sealing gasket 100 to seal the pyrotechnic chamber.

FIG. 1 c is a view of a detail of a variant embodiment of the mortar round according to the invention. This variant embodiment of FIG. 1 c avoids damage to the body sealing gasket 96 as the rear body 50 is being mounted inside the casing 30 of the propulsion system. Specifically, when the rear body 50 is outside the casing 30, the uncompressed body sealing gasket 96 expands and its diameter becomes greater than the diameter D1 of the internal surface 31 of the casing 30. As the rear body 50 is being inserted into the casing 30, first of all the casing edge 32 butts against the body sealing gasket 96 and then, as the rear body continues to slide into the casing, said body sealing gasket 96 expands again into the other ring groove 90 and further effort has to be applied once again to continue to slide the rear body into the casing, and this may damage the body sealing gasket 96.

In order to avoid damage to the body sealing gasket 96, in this variant of FIG. 1 c, the internal surface 31 of the casing of diameter D1 is extended toward the casing edge 32 by another surface 310 of diameter D30 greater than the diameter D1, the rear body 50 comprising, on the end surface 54 side, a circular surface of the same diameter D1 extending toward the shoulder 51 in the form of another surface of greater diameter equal to the diameter D30.

The diameter D30 needs to be at least the outside diameter of the uncompressed body sealing gasket 96, if not greater.

In the case of FIG. 1 b, damage to the body sealing gasket 96 can be avoided by creating, on the surface 31 side, chamfers on the casing edge 32, on the edge of the hole 80 for the pin 70 and on the edges of the other groove 90.

Hereafter, and to simplify the description, we shall consider only the embodiment of FIG. 1 b.

The operation of the device for automatically hardening the munition/propulsion system mechanical connection according to the invention in an application to a mortar round is explained hereinafter.

FIGS. 1 a, 1 b, 2 a and 2 b show the mortar round during the phase of storage or handling by personnel prior to firing without any attack on the pyrotechnic charge that could activate it.

During this storage phase, the first mechanical connection is in the activated state.

FIGS. 3 a and 3 b show two respective steps in the operation of the mortar round of FIG. 1 a as pressure in the propulsion system rises prior to firing.

In this operating configuration depicted in FIGS. 3 a and 3 b, known as the deconfinement configuration, the pyrotechnic charge, following an external attack, has been prematurely initiated, causing an increase in pressure by gases appearing in the pyrotechnic chamber 33 corresponding to the volume of the propellant pyrotechnic charge with the thermal protection walls 40, 44 (or combustion inhibitor).

The pressure generated in the pyrotechnic chamber 33 tends to cause the moving end wall 60 to move toward the surface 54 of the munition rear body 50, thereby compressing the spring 64. The fluid-tightness of the pyrotechnic chamber 33 is still afforded by the end wall sealing gasket 100 mounted on the periphery of the moving end wall 60.

As it continues to move toward the munition body 12, the moving end wall 60 comes into abutment against the rear surface 54 of the munition rear body 50, thus taking up the clearance J1. An additional increase in pressure in the pyrotechnic chamber causes forces F to be applied by the moving element 60 to the munition rear body 50 and stress to be applied to the shear pins 70.

The shear pins 70 are rated to withstand forces Fg that are small with respect to the pressure that can be experienced by the pyrotechnic chamber. Once these forces Fg have been exceeded, the pins 70 break, allowing the casing 30 of the propulsion system to disengage and move away from the munition. The first mechanical connection is then in the deactivated state.

The separation of the casing from the munition body releases into the surrounding environment the pyrotechnic charge 34 with its thermal protection walls 40, 44 and the hot gases Gc produced by pyrotechnic combustion.

At the end of this operation the propulsion system is considered to be “deconfined”.

FIG. 4 a depicts the mortar round of FIG. 1 a in a firing phase. FIG. 4 b shows an external view of the region of connection between the munition and the propulsion system of the mortar round of FIG. 4 a.

For this phase of firing by a mortar, the mortar round is fitted on the outside of the propulsion system with a propulsive tail (not depicted in the figures) which ejects the mortar round from the mortar tube. This phase of ejection of the mortar is known as the internal ballistic phase.

At the start of the internal ballistic phase, when the mortar round fitted with its propulsive tail strikes the end wall of the mortar, activation of the propulsive tail produces an ejection thrust that is transmitted to the munition by the propulsion system. During this internal ballistic phase, the propulsion system is not yet initiated.

The ejection thrust from the propulsive tail generates a force which, because of the inertia of the munition, drives the propulsion system 20 against the munition body 12. Instantaneously, all the pins 70 become sheared, switching the first mechanical connection from the activated state to the deactivated state. The edge 32 of the casing 30 of the propulsion system comes into abutment with the shoulder 51 of the munition body, thus taking up the clearance J2. The clearance J1 between the end surface 54 of the munition rear body 50 and the other face 62 of the moving end wall is smaller but still exists, this clearance J1 being, as described earlier, greater than the clearance J2 (see FIG. 4 a). The other ring groove 90 on the internal surface 31 of the casing 30 now finds itself facing the ring groove 56 on the surface of the munition rear body 50, and this allows the retaining ring 58, which was mounted under stress in the ring groove 56, to expand into the other ring groove 90 in order once again to secure the propulsion system 20 to the munition body 12 in terms of translational movement and more rigidly than it was under the action of the pins 70. In this munition firing phase, the second mechanical connection switches from the deactivated state to the activated state.

The two pegs 76, 78 remain closely fitted into their respective notches 72, 74 without any play still, in spite of the shearing of the pins 70, preventing the casing 30 of the propulsion system from rotating against the munition body 12 (see FIG. 4 b).

In this configuration, the second mechanical connection between the munition 10 and the propulsion system 20 is said to be hardened, which means to say that the initiation of the propulsion system can be authorized.

FIG. 5 a depicts the mortar round of FIG. 1 a in a phase of the initiation of its propulsion system. FIG. 5 b is a view of a detail of FIG. 5 a.

The propulsion system 20 once initiated generates a pressure in the pyrotechnic chamber 33 which tends to compress the spring 64 and to cause the moving end wall 60 to move toward the end surface 54 of the munition rear body 50. The fluid-tightness of the moving end wall 60 moving in the casing 30 of the propulsion system is afforded by the end wall sealing gasket 100.

The movement of the moving end wall 60, driven by the pyrotechnic chamber 33, continues until its other face 62 comes into contact with the end surface 54 of the munition rear body 50, thus taking up the remaining clearance J1.

As soon as the moving end wall 60 comes into abutment against the end surface 54 of the munition rear body 50 and the pressure in the pyrotechnic chamber 33 continues to increase, tending to cause the munition body 12 to leave the casing 30 of the propulsion system, the retaining ring 58 is in turn placed under shear stress between the casing 30 and the munition rear body 50. This retaining ring 58 is rated to withstand this force. Propulsion system operation in this phase is said to be nominal.

FIG. 6 shows a variant embodiment of the hardenable mechanical connection according to the invention for the mortar round of FIG. 1 a.

In this embodiment of FIG. 6, the shear pins 70 and the retaining ring 58 are secured to the munition via a propulsion system end wall 110 which is itself secured to the propulsion system.

In this embodiment of FIG. 6, the propulsion system 20 comprises the propulsion system end wall 110 of circular cylindrical shape in the form of a collar closed by an end wall 112 in a plane perpendicular to the axis ZZ′. As in the munition rear body 50, the circular cylindrical exterior surface of the end wall 110 comprises the shoulder 51, the holes 82 for the pins 70, the groove 56 containing the retaining ring 58 and the groove 94 containing the sealing gasket 96. The face of the end wall 112 on the propulsion system side has the same role as the end surface 54 in the previous embodiment.

A circular cylindrical internal part 120 of the propulsion system end wall 110 has a screw thread 121 for the screw-fastening of the munition rear body 50 which likewise has a screw thread 122 that can be screwed onto the screw thread 121 of the propulsion system end wall 110.

In this variant of FIG. 6, the munition is secured to the propulsion system by the screw threads 121, 122, the device for automatically hardening the munition/propulsion system mechanical connection being fully incorporated into the propulsion system. The propulsion system, in this variant of FIG. 6, is still endowed with the deconfinement function whether or not it is connected to the munition body 12.

In order to safeguard the mortar round against potential impacts, for example caused by droppage, which could shear the pins 70 as in the case of the ejection of the round when fired, the mortar round may be equipped during its storage, transport and handling phase, with a belt 130 that locks against breakage of the first mechanical connection.

FIG. 7 depicts a partial view in axial section through the mortar round of FIG. 1 a comprising a belt that locks against breakage of the mechanical connection.

The belt 130, in the form of a tube with an outside diameter D5 greater than the diameter D2 of the external surface of the propulsion system and of the munition, partially surrounding the munition body 12 and the casing 30, comprises an interior part 140 in the form of a collar inserted into the clearance J2 to prevent the edge of the casing 32 from moving closer to the shoulder 51, thus effectively protecting the shear pins 70 against potential droppage of the mortar round while at the same time maintaining the possibility to deconfine the propulsion system 20 in the event of an external influence such as a fire.

The mortar round is intended to be placed into a launch tube having an inside diameter equal to (or slightly greater than) the diameter D2 of the munition equipped with its propulsion system. The mortar round cannot be introduced into the launch tube until the belt 130 has been removed, because of the diameter of the belt D5 which is greater than the inside diameter D2 of the launch tube. This is an additional safety feature that prevents the munition from being launched unless the belt 130 that blocks against breakage of the first mechanical connection has first been removed.

The pegs 76, 78 and the notches 72, 74 can be produced in different ways, such as a pin or key in a groove or key way, a splined shaft in a splined hub, or any other means securing the munition to the propulsion system against rotation but allowing a translational movement along the longitudinal axis ZZ′.

In the mortar round according to the invention, the shear strength of the self-hardenable second mechanical connection afforded by the retaining ring 58 when inserted into the other ring groove 90 is far higher than that of the first mechanical connection afforded by the shear pins 70, and so deconfinement of the propulsion system 20 is achieved with a low pressure of gases in the pyrotechnic chamber which is well below the pressure needed in deconfinement devices of propulsion systems of the prior art. 

1. A self-propelled munition intended to be fired against a target, comprising: a munition having a munition body extended by a munition rear body of circular cylindrical shape of diameter D1, along a longitudinal axis ZZ′, a propulsion system of the munition having a casing in the form of a tube of circular cross section of diameter D2, of axis of revolution coincident with the longitudinal axis ZZ′, the casing, having an internal surface of the same diameter D1 as the munition rear body, being able to slide over said munition rear body along said longitudinal axis ZZ′, the casing containing a pyrotechnic propulsion chamber intended to be activated upon firing, wherein it comprises at least two mechanical connections each able to adopt an activated state that secures the propulsion system to the munition or a deactivated state that releases the propulsion system from the munition, the first mechanical connection comprising several shear pins, evenly distributed about the longitudinal axis ZZ′, inserted into the casing of the propulsion system and into the munition rear body, said first mechanical connection moving from an activated state to a deactivated state through the breakage of the shear pins, and the second mechanical connection having a ring groove around the munition rear body in a plane perpendicular to the longitudinal axis ZZ′, another ring groove on the internal surface of the propulsion system casing, a retaining ring inserted in the ring groove, the retaining ring being configured to expand into the other ring groove from the diameter D1 to a diameter D4 that is greater than the diameter D1, and place said second mechanical connection in the activated state.
 2. The self-propelled munition as claimed in claim 1, wherein, in a storage phase, the first mechanical connection is in the activated state, the intact pins securing the propulsion system to the munition in terms of rotational and translational movement.
 3. The self-propelled munition as claimed in claim 1, wherein, in a munition firing phase, a sliding of the casing over the munition rear body toward said munition body places the first mechanical connection in the deactivated state by the breakage of the shear pins, the second mechanical connection in the activated state through the expanding of the retaining ring into the other ring groove which comes to face the ring groove during said sliding of the casing over the munition rear body.
 4. The self-propelled munition as claimed in claim 1, wherein, during a propulsion system deconfinement phase, a sliding of the casing over the munition rear body away from the munition body through an increase in pressure caused by the gases of combustion in the pyrotechnic chamber, places the first mechanical connection in the deactivated state by the breaking of the shear pins and the pyrotechnic chamber in contact with the external surroundings in order to release the combustion gases.
 5. The self-propelled munition as claimed in claim 1, wherein the munition rear body comprises, on each side of the longitudinal axis ZZ′, two notches and the propulsion system casing comprises two pegs, one peg being inserted into one respective notch on each side of said longitudinal axis ZZ′ to secure the munition and the propulsion system in terms of rotation about the longitudinal axis ZZ′.
 6. The self-propelled munition as claimed in claim 1, wherein the casing is delimited, on the munition side, by a casing edge in a plane perpendicular to the longitudinal axis ZZ′.
 7. The self-propelled munition as claimed in claim 1, wherein the munition body, of circular cylindrical shape having the same outside diameter D2 as the casing of the propulsion system, is extended inside said casing by the munition rear body in the form of a cylinder of circular cross section of diameter D1 forming an annular shoulder in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body ending in the casing in the form of an end surface in another plane perpendicular to the longitudinal axis ZZ′.
 8. The self-propelled munition as claimed in claim 1, wherein the casing contains a pyrotechnic chamber containing a propellant pyrotechnic charge, the pyrotechnic chamber comprising walls affording thermal protection to the pyrotechnic charge, one thermal protection wall in the form of a tube, in contact with the internal surface of the casing and closed, on the munition side, by another thermal protection wall perpendicular to the longitudinal axis ZZ′.
 9. The self-propelled munition as claimed in claim 8, wherein the casing of the propulsion system comprises, at the same end as the other thermal protection wall of the pyrotechnic chamber, a circular cylindrical moving end wall of the same diameter D1 as the internal surface of the casing, of axis of revolution coincident with the longitudinal axis ZZ′, having two faces in planes perpendicular to the longitudinal axis ZZ′, one face in contact with the thermal protection wall and another face on the munition rear body side having a circular recess for keeping a coil spring along the longitudinal axis ZZ′, the spring being inserted between said moving end wall and the end surface of the munition rear body in order to ensure a distance L1 forming a clearance J1 between the other face of the moving end wall and the munition rear body.
 10. The self-propelled munition as claimed in claim 6, wherein the casing of the propulsion system comprises holes near the casing edge in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body having other respective holes in the same plane perpendicular to the longitudinal axis ZZ′ facing the holes in the casing of the propulsion system for the forcible insertion of the pins, the positions of the holes near the casing edge and those of the other holes in the munition rear body being such that when the pins are inserted into the respective holes in the casing and the munition rear body, the shoulder of the munition body and the casing edge are separated by a distance L2 to form a clearance J2.
 11. The self-propelled munition as claimed in claim 10, wherein the clearance J2 is smaller than the clearance J1 so that when the pins have sheared upon firing, the casing edge and the shoulder coming into contact, there is still a space between the munition rear body end surface and the other face of the moving end wall.
 12. The self-propelled munition as claimed in claim 1, wherein the shear strength of the second mechanical connection is greater than the shear strength of the first mechanical connection.
 13. The self-propelled munition as claimed in claim 1, wherein the shear pins and the retaining ring are secured to the munition by a propulsion system end wall which is itself secured to the propulsion system.
 14. The self-propelled munition as claimed in claim 13, wherein the propulsion system end wall is in the form of a collar closed by an end wall in a plane perpendicular to the longitudinal axis ZZ′, the circular cylindrical exterior surface of the end wall comprises the shoulder, the holes for the pins, the groove containing the retaining ring and the groove containing the body sealing gasket, the face of the end wall on the propulsion system side having the same role as the end surface.
 15. The self-propelled munition as claimed in claim 14, wherein a circular cylindrical internal part of the propulsion system end wall has a screw thread for the screw-fastening of the munition rear body which likewise has a screw thread that can be screwed onto the screw thread of the propulsion system end wall.
 16. The self-propelled munition as claimed in claim 1, wherein during its storage, transport and maintenance phase, it is fitted with a belt that locks the first mechanical connection in the activated state.
 17. The self-propelled munition as claimed in claim 16, wherein the locking belt, in the form of a tube with an outside diameter D5 greater than the diameter D2 of the external surface of the propulsion system, partially surrounding the munition body and the casing, comprises an interior part in the form of a collar inserted between the casing and the munition body to prevent them from moving closer to one another.
 18. The self-propelled munition as claimed in claim 7, wherein the casing of the propulsion system comprises holes near the casing edge in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body having other respective holes in the same plane perpendicular to the longitudinal axis ZZ′ facing the holes in the casing of the propulsion system for the forcible insertion of the pins, the positions of the holes near the casing edge and those of the other holes in the munition rear body being such that when the pins are inserted into the respective holes in the casing and the munition rear body, the shoulder of the munition body and the casing edge are separated by a distance L2 to form a clearance J2.
 19. The self-propelled munition as claimed in claim 8, wherein the casing of the propulsion system comprises holes near the casing edge in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body having other respective holes in the same plane perpendicular to the longitudinal axis ZZ′ facing the holes in the casing of the propulsion system for the forcible insertion of the pins, the positions of the holes near the casing edge and those of the other holes in the munition rear body being such that when the pins are inserted into the respective holes in the casing and the munition rear body, the shoulder of the munition body and the casing edge are separated by a distance L2 to form a clearance J2.
 20. The self-propelled munition as claimed in claim 9, wherein the casing of the propulsion system comprises holes near the casing edge in a plane perpendicular to the longitudinal axis ZZ′, the munition rear body having other respective holes in the same plane perpendicular to the longitudinal axis ZZ′ facing the holes in the casing of the propulsion system for the forcible insertion of the pins, the positions of the holes near the casing edge and those of the other holes in the munition rear body being such that when the pins are inserted into the respective holes in the casing and the munition rear body, the shoulder of the munition body and the casing edge are separated by a distance L2 to form a clearance J2. 